SIP trunks are virtual phone lines that operate over the Internet using the SIP (Session Initiation Protocol) VoIP (Voice over IP) technology. A SIP trunk is the modern equivalent of a digital trunk from the old PSTN (Public Switched Telephone Network).
Years ago, businesses would purchase analog or digital phone lines (E1 or PRI) from a telecommunications provider and connect them to an on-premises PBX (Private Branch Exchange), the physical system that managed all office phone calls. Today, instead of relying on traditional telecom services, companies can subscribe to a SIP trunking service through their Internet Service Provider (ISP) and connect it to a VoIP/IP PBX—either hosted in their office or in the cloud.
The term “trunk” comes from traditional telephony and refers to a group of phone lines working together. Not all SIP trunks are the same—some still rely on physical connections to the office, as offered by providers like Claro or Movistar. Others are fully cloud-based, meaning they function as an internet service without being tied to any physical infrastructure or specific location.
La Troncal SIP fija es un servicio que ofrecen los proveedores de telecomunicaciones, usualmente a través de un canal de fibra óptica que va de sus instalaciones hasta tu oficina, y para acceder al servicio necesitas conexión física a un equipo instalado por el proveedor.
Esta opción es ideal si tus comunicaciones operan desde un equipo instalado en tus oficinas, mas no es el ideal para operar tus comunicaciones desde la nube, ya que tendrías que enviar las llamadas desde tu oficina al Internet lo cual es completamente posible pero va a requerir de algunos ajustes adicionales.
A Mobile SIP Trunk is a fully virtual telephony service provided over the internet. It functions just like a fixed SIP trunk but without requiring a physical fiber-optic connection or on-premises hardware. Instead, it is delivered as a cloud-based service, offering businesses greater flexibility and mobility.
One of the key advantages of a mobile SIP trunk is that it can be accessed from anywhere—not just from a specific location where the provider has installed its equipment. This makes it the perfect solution for companies using a cloud-based virtual PBX, as no additional hardware is needed. Simply configure it, and you’re ready to go.
Essential Requirements to Use a SIP Trunk in Your Business
If your on-premises PBX supports SIP, you can connect the SIP trunk through your local area network (LAN)—the same network that links your computers.
For a fixed SIP trunk connection, you will need:
The setup process typically follows a standard configuration similar to the diagram below, ensuring secure and reliable communication between your PBX and the SIP provider.
If you are connecting an on-premises PBX to a virtual SIP trunk, the setup is even simpler. You only need:
However, security considerations are crucial. Since your communications will traverse the public internet, you must take precautions to prevent unauthorized access and cyber threats. It’s highly recommended to consult with an expert before exposing SIP services directly to the internet.
A typical connection to a virtual SIP trunk follows a secure setup, ensuring encrypted communication and proper firewall configurations, as shown in the following diagram.
If you’re using a cloud-based PBX like Audara DreamPBX, integrating a virtual SIP trunk is seamless and highly efficient. Since your PBX operates entirely in the cloud and is accessible from anywhere, there’s no need for on-premises hardware—only a secure and properly configured connection.
To ensure a reliable and secure setup, consider the following:
A typical connection between a virtual SIP trunk and a cloud-based PBX is straightforward. However, security configurations—such as access controls and traffic encryption—should always be in place, even if they are not shown in simplified diagrams.
In practice, choosing the right SIP trunk depends on your specific business needs. If you already have physical phone lines in your office and want to retain your existing number—especially if it’s well-known to your customers—a fixed SIP trunk may be the best option. On the other hand, if you’re launching a new service, opting for a virtual SIP trunk can be faster, easier, and more flexible.
Changing your business phone number isn’t always advisable, as it may disrupt customer communication. However, virtual SIP trunks offer a significant advantage: the ability to acquire local or international phone numbers (DIDs), allowing your business to establish a global presence without major costs. For example, you could have a primary number in Mexico, an alternative number in Miami, and another in Spain, all seamlessly managed from your main office. To maximize these benefits, check with your provider about virtual DID services.
Both virtual PBXs and cloud-based contact centers, such as those offered by Audara, support fixed and virtual SIP trunks, ensuring complete flexibility. If you need expert advice to choose the best option for your business, feel free to reach out—we’ll be happy to help!
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